1. Bradykinin is considered to be an important mediator of pain and hyperalgesia associated with injury and inflammation. Psychophysical studies were conducted in a patient with complete kininogen deficiency to determine whether the absence of bradykinin was associated with abnormalities in pain sensibility. Pain evoked by heat stimuli to the thenar eminence was tested before and after a localized burn, which has been shown to cause hyperalgesia in normal subjects. In addition, pain evoked by intradermal administration of bradykinin (0.1–10 μg) to the forearm and the effects of bradykinin on pain induced by heat stimuli were studied. The patient rated the intensity of pain evoked by all heat stimuli relative to the pain induced by a 3s 45°C stimulus.

2. The patient's heat pain threshold (45°C) in the glabrous skin was similar to that of age-matched control subjects (n = 5) and to that previously observed in younger control subjects.

3. The burn resulted in a decrease in pain threshold and an increase in pain induced by suprathreshold stimuli. The magnitude of hyperalgesia was within the range observed in the age-matched control subjects and in younger control subjects. Thus, kinins are not essential for the development of hyperalgesia after heat injury.

4. In control subjects, intradermal injections of bradykinin produced pain and hyperalgesia to heat stimuli. In the patient, intradermal bradykinin injections induced minimal pain and no hyperalgesia to heat stimuli. Thus, congenital absence of kininogens may be associated with a deficiency in bradykinin receptors.

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